Moving child from cot to crib

I don't think there's any specific age that you "can" but more towards when you "should"! Some children don't like cribs/baby cots/playpen in the first place - like my son. We started co-sleeping since birth on my sofa bed, then we switched to spring mattresses on the floor and subsequently upgraded to foam ones when he started jumping around a lot. The age you should move is when your child can no longer fit comfortably and/or safely in the crib! Either because your child learned how to climb out, or simply outgrew the length of it.